The organic light emitting device (OLED) includes a pixel electrode, a common electrode, and an organic light emitting member formed therebetween.
In this organic light emitting device, electrons injected from a cathode electrode and holes injected from an anode electrode are coupled at an emitting layer of an organic light emitting member, and excitons are thereby formed. The formed excitons emit light while discharging energy.
Accordingly, since the OLED does not require an additional light source, the power consumption of the OLED is low. Also, the OLED has a fast response speed, a wide viewing angle, and a superior contrast ratio.
The OLED may be classified as a passive matrix OLED and an active matrix OLED according to a driving type.
Among them, the active matrix OLED, which has thin film transistors as switching elements and driving elements for individually driving each pixel, may be advantageous in the aspects of high resolution, power consumption, and the capacity to be produced with a large size.
Also, the organic light emitting device may be classified as a top emission OLED and a bottom emission OLED according to emission type.
Among them, in terms of schematic structure, the bottom emission organic light emitting device includes a thin film transistor array panel. The thin film transistor array panel includes a plurality of thin film transistors connected to first signal lines and second signal lines, a plurality of color filters formed on the thin film transistors, and an over-coating film covering the color filters.
Also, first electrodes made of indium tin oxide (ITO) or indium zinc oxide (IZO) are formed on the over-coating film, a partition having openings exposing a portion of each first electrode is formed on the first electrodes, and an emitting layer and a second electrode are sequentially formed on the first electrodes in the openings.
In the bottom emission organic light emitting device, a technique in which protrusions and depressions are formed in the surface of the over-coating film has recently been developed. In this structure of the bottom emission organic light emitting device, light loss by total reflection may be reduced on the interface surface between the first electrodes and the over-coating film to thereby increase light extracting efficiency. A iso, the area of the light emitting member is increased, thereby reducing current density.
On the other hand, reflection is generated in the interface surface between the first electrodes and the over-coating film due to a difference in refractive indexes of the first electrodes and the over-coating film such that a micro-cavity effect is generated in the bottom emission organic light emitting device.
For example, when forming the first electrodes made of IZO, and the over-coating film made of polyacrylate, the refractive index of the first electrodes is about 2.0 but the refractive index of the over-coating film is about 1.5. Therefore, reflection is generated in the interface surface between the first electrodes and the over-coating film.
The micro-cavity effect is a phenomenon in which light of a predetermined wavelength is enhanced due to constructive interference generated in a micro-cavity where a space is formed between two reflection surfaces for reflecting the light. In the bottom emission organic light emitting device, a space from the interface surface between the first electrodes and the over-coating film to the second electrode is the micro-cavity.
Here, the wavelength that is enhanced in the micro-cavity is proportional to the length of the micro-cavity. Accordingly, to enhance the color red that has a relatively longer wavelength than the color blue, it is preferable that the length of a micro-cavity provided in a red pixel is larger than the length of a micro-cavity provided in the blue pixel.
To achieve this objective, different lengths of micro-cavities are formed according to different colors by controlling the thickness of the over-coating film or the first electrodes according to the emitting type of the display device.
However, additional processes to form the different lengths of the micro-cavity according to the colors are needed such that the manufacturing cost when implementing the additional processes is increased.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.